Direction finding



May 11, 1937. w KUNZE 2,079,620

DIRECTION FINDING Filed'Feb.A21, 1931 2 Sheets-Sheet 1 26 y 27 s s i? 3Inl/enrich Dn /z'lly Kanye Perfl/MW?? Jl tt orne'u.

May 11, 1937. WgKUNZE v2,079,620

DIRECTION FINDING Filed Feb. 21, 1931 Y 2 sheets-sheet 2 37 u y Figure4' DZ fe/'liar Dr. willy- Kunj'e bothears 'ments which I have observedcertain advan ages are presented in the use of the maximum method'Patented u May Y 11, 1937 Willy Kunze, Bremen, G

'marine Signal Company,

poration of Maine Application February 21,

April 30, 1930 In Germany ermany, assigner to Sub- Boston, Mass., a cor-1931, SerialNO. 517,510

Claims. (Cl. 177-386) The present invention' relates to the art ofdetermining :the direction of a source of compres# sional waves; andmore particularly to sound waves propagated in air or water medium inwhich a group Aof sound receivers are used and in which the sound energyarriving at each receiver is brought-into the same phase at theindieatingv device. In arrangements of this nature it is common practicein the art to use a group of electrically responsive acoustic receivingdvices spaced'apart ina definite' geometric configuration a'nd conductthe electric energy created by thesound waves arriving at each receiverthrough retardation lines to a pair of telephone devices or 'anindicator.v In lsuch apparatus theY retardationv lines form a so-calledelectric compensator in which a switch mechanism is provlded tocompensate for a variation ofthe direction of the wavefront arriving atthe receivers.

y In this way, it is possible to turn the compensator .switch mechanismuntil the receivers are compensated for any particular direction of thewave front. When the receivers are so campen# sated that the wave frontfor which they are adjusted" corresponds to the actual Wave front of 25.the sound being received, a maximum sound intensity is present inthetelephones or listening devices.- Y

In the ypast in such apparatus two methods of compensation 'have'generally been used, one in which the observer notes the position ofthe 1 binaural image and the other in which the obserjvatlon is made byobserving the maximum sound intensity.

3 In systems employing the so-called binaural method the receivers ofone group are connected is actually distributed over an angle subtending,ship is approximately in the same line, or nearly the same line, it isalmost impossible to distinguish the diffrent vessels and set upon eachseparately with the maximum method. The sounds of the two vessels blendto-. gether over the angle betwen the two vessels from the listeningsource and it is practically impossible to obtain a true setting of themaximum intensity of the sound from any one-of the vessels. This mightnaturally be expected since the sound l0 the line of the two vesselsfrom the listening source. In these cases the binaural method oflistening often vproves very advantageous since the sound image ofeach'vessel is4 independent l, and separable from eachother, andalthough other disturbing sounds may be present, there will be adistinct shift from a lateral to a central image of one group of soundseven though the other group are present in the same field.

I have found, however, that by the use of a 20 highpass filter the fieldof each individualvessel may be considerably narrowed and if the othervessel is not within this narrow range, a setting by the maximum methodmay be made. Where, however, the two vessels are positioned in the samenarrow field according to my invention the filter is dispensed with andthe binauralmethod sels from the listening used.

with one telephone going'` to one of the ears of the observer and thereceivers ofthe other group are connected to a second telephone going tothe other ear of the observer.

With the maximum method, on the other hand,

the receivers are all connected to both telephones so'that the samemixed sound wave arrives at of the observer. According to e and certainother advantages are presented in the use of the binaural method. D Thecombination of these advantages in a sin- .50 'gie-devicefor the purposeof determining the direction of' a source of sound'or compressionalpasses.Y

.of all frequencies reach the In view of thev fact thatA the eliminationof the lower frequency sounds sharpens the maximum intensity, it ispossible by this method to obtain a much more accurate setting andobservation of the direction of the source of sound waves. In employingthis feature it is possible to listen, first, without the use of afilter in which case sounds ears of the observer of the indicatingdevice, and it is then possible, after the character of the vessel hasbeen deter.- mined by listening to the natural sounds, to cut 40 out allthe sounds ofthe lower frequencies and accurately determine thedirection of the source with only the higher frequencies. I have foundin some cases that the use of av filter diminishes the sound intensityarriving at the indicating de- 4, vice. This is perhaps particularlytrue where the greater part of thesound source is made of sounds oflower frequencies from that which the filter In such cases an amplifieris used in connection with the. lter to bring up the sounds to 5| normalValue.

,wave is the Vsubject .matter of the present invention.

` In particular, in listening to a number of vessels in thesame field,where the direction of the'ves- The filter usedin-the present inventionmay be' -one which passes frequencies above eight hundred cycles, but Iprefer ir most cases to use a highpass filter which has a highercut-off, for in- 5 the filter stance, at fteen hundred cycles. It isvery diiicult to obtain a binaural setting for frequencies'above fifteenhundred cycles, and in this range, therefore, the maximum-minimum methodis most effective.

Y The present invention will be described in particular in connectionwith the drawings in which Fig. 1 illustrates the sound intensity fieldwith both low andv high frequencies present, Fig. 2 illustrates thesound intensity field with thel use of av high-pass lter, Fig. 3 showsschematically a circuit arrangement and Fig. 4 shows a modification ofthe circuit shown in Fig. 3.

In Fig. 1 the line 4IJ',` having dots I, 2, 3, 4, 5 and 6, indicates thereceivers arranged along this line on the dots just mentioned. 'I'hecurve 'I in this case shows the relative intensities with which sound isreceived coming from a direction in the same plane as the plane of thepaper. For instance, a sound coming from the direction of the line 9, I2will have an intensity corresponding to the vector value of the length9,' I2. A sound coming from the direction 9, II will have the intensitycorresponding to the vector length 9, II.

In Fig. 2 where the curve 8 corresponds to the curve 1 with theexception that the lower frequencies'have been cut out'by the lter, theline I0, I4 shows the relative intensity of the ysound received from adirection of III, I4. Comparing Figs. 1 and 2, if the vector lengths I0,I3 and I0, I4 are the same as the vector lengths 9, II and 9, I2,respectively, the figures indicate that in the case of Fig. 1 for thedecrease in the same intensity of sound the angle is u' while in Fig. 2-this same angle is a. In the case of Fig. 2 the intensity drops oil'quickly wi-th small variations in angles, whereas in Fig. 1 it drops offmuch more slowly. i

With the use of high-frequency filters, there is often present secondaryor auxiliary maximum in the shape of small lobes similar to the lobes of8 in Fig. 2. These lobes are apt to cause an ambiguity of direction andthis is overcome in the present application by the use of the binauralmethod as 'a check to eliminate these ambiguities. The binaural imagewill only be produced with the maximum lobe so that if the compensatoris set on a secondary lobe, this will easily be determined by switchingto the binaural method which will indicate whether a binaural image isory is not obtained.

In Fig. 3 there is illustrated diagrammatically by I, 2', 3, 4, 5 and 6corresponding to the same numerals in Figs. 1 and 2. If the group ofreceivers I to 6, inclusive, are rotated about an axis 90 so. that theirline is made to coincide with the wave front of the approaching sound,the electrical energy in the circuit 2l connected to the receivers I to6, inclusive, through the transformers I to 20, inelusive, respectively,will be impressed upon the telephone 22 either through the filterindicated as 23 or over the straight transmission line 4I. The lter 23comprises the inductances 30 to 33, inclusive, in shunt and the capacity26 to 29, inclusive, in' series between each shunted inductance.Switches 24 and 25 are provided to throw or the transmission line inbetween Vthe telephone 22 and the `receiving circuit 2 I In Fig. 4 `thecomplete arrangement of the circuit in which a compensator using eitherthe binaural or the maximum-minimum method and a filter and an amplifierassociated together is shown..- In this figure the receivers areindicated `to the right, both telephones shown a group of 4six receivers.tardation lines 44 and 45. 5, inclusive,

In this system, therefore, the eiective binaural` base is a distancebetween-'two adjacent receivers. The system just described is chosenbecause this will give a sufficient binaural base to be used in checkingthe true maximum from auxiliary max# imum and'also iniaiding thedetermination of the direction of a source of sound when the two vesselsare in the same field.

A proper switch dicated by 46 and 49, 50, 5I, 52 and 55, 56 and 41, toadjust the contacts 48, corresponding contacts 53, 54, at various pointsalong the respecfrom listening which includes the mier 23 and theampliler A in front of the telephones 62 and 63. The amplier A isconnected to the circuit at the stances the telephone 63 is groupofsound 'receivers while the telephone 62 is operated by the right groupof sound receivers. When the switches 60 and 6I are thrown thrown "inparallel and are operated by both reand both groups of receivers.

When the switch 60 is thrown to the right, both retardation lines 44 and45 are connected through the short leads 80 and 8| to the input point 82of the filter. It will be noted that the common 83 is at all timespermanently connected on one side to the Iamplifier .as at 84 and on theother side to the common lead to the right and left headphones 62 and63. The output lead 86 of the lter with lthe common 84 form the input tothe-amplifier. The output to the amplifier, leads -81 and 88, when theswitch 6I is-in the position shown in Fig. 4 to the head telephonethroughthe leads 88 and90, respectively. In this arrangement justdescribed' both the lter and the amplier are in circuit and the twotelephones are connected in parallel, -botlreceiving the. same input andtherefore. providing onlyV a,

The compensator 'shown at 43 is,

mechanism is provided, as in- I operated by the left v 62 vand 63 are onthe right lead 64 and the left lead 64, re-

` justment on the I multispot listening spectively.` The leads 64conduct the impulses through the switch 6l to the telephone head pieces62 and 63 by'means of the leads 89 and 90. The common 83 remains asbefore connected to the common to the two telephones. In this positionthe telephone 63 is connected to the retardation line 44, and thetelephone 62 to the line 45, and a binaural listening is thereforepossible.

In the method employed in the present case, the operator can eitherlisten, first, by the binaural method or by the maximum method. If helistens by the maximum method, he preferably may use the filter 23 andthe amplifier A to amplify the 4high-frequency sounds which may besomewhat weak if they are not the predominant frequencies from thelistening source. In order thereafter to determine whether any ambiguityof direction exists, he may throw the switches 60 and 6l to the left andcheck his observation by the binaural method.

This is perhaps the preferable manner of operating the present systemalthough it is possible and perhaps under certain circumstancesdesirable to employ the binaural method when the vessel to be vessel. Inthis case the binaural method may alone be employed or the binaural incombination with the maximum method may be employed as described justabove.

There are a number of advantages i'n first determining the approximatedirectionof the source of sound without the use of a filter and thenusing the filter in the final steps. Since without the use of the filterthe true character of the sound is more clearly observable, it ispossible frequent- 'ly in cases where more than one sound is in thellistening eld to concentrate on one of the sounds for an approximatesetting and then complete the observationby a more accurate adsoundwhichis first observed. In this way even though two sounds are somewhat neartogether as, for instance, when two ships are within the listening rangeof the apparatus within a few degrees of one another, it is frequentlypossible to make an accurate determination of the position of oneeliminating the position of the other.

In addition to this, however, a further ad'- vantage is obtained inmaking an approximate determination initially without the use of a lter.While the filter image to a considerable degree, it provides, however, anumber of secondary or auxiliary maxima4 which might sometimes bemistaken for the chief maximum if the compensator is set with the filterinitially used. Omitting the lter initially, the chief maximum can bereadily determined within a number of degrees, and then using the lter,this maximum can be observed very-accurately.

In addition there is a further utility in observing the sound initiallywithout the use of a filter. While most vessels in So-called submarineradiate sounds of practically all frequencies, still it sometimeshappens that certain frequencies are not produced. If a vessel did notemit much hig'h frequency sound, the use of a filter initially wouldmake it appear that no. source was within the listening range and may,therefore, be difficult at firstvto detect the source.. In this casethe. initial observation is quite important. It is also true thatfrequently the observed is in the vicinity of another itself sharpensthe maximumA maximum with a filter on account of its sharpness will bepassed over in making an observation. The maximum without the filterbeing quite broad furnishes a good initial observation for beginning theaccurate determination of the direction -of the source.

Having now described my invention, I claim: I

1. In combination, a plurality of spaced receivers, a pair of telephonereceivers, a compensator for bringing the sound received at saidreceivers into substantially the same phase to produce a maximum soundintensity at the telephone, a filter and an amplifier adapted to beassociated therewith at the output of said compensator, and meansconnecting said filter and amplifier in circuit after the compensator,and said telephone receivers as a singleY unit in the circuit after theother elements when the filter and amplifierare used and connecting saidtelephone receivers individually at the said output when the filter andamplifier are not used.

2. In combination, a plurality of spaced re-v ceivers, a compensator,means for using said compensator for the binaural or maximum-minimummethod, a high pass filter, a pair of telephone receivers connected tosaid compensator, and means for. connecting the filter in circuit beforesaid telephone receivers in using the maximum-minimum method andomitting the filter in using the binaural method.

3. In combination, a plurality of spaced receivers, a compensator, meansfor using said compensator for the binaural or maximum-minimum method, ahigh pass filter and amplifier associated therewith at the output ofsaid compensator, a pair of telephone receivers, and means forconnecting the filter and amplifier in circuit between the compensatorand said telephone receivers 'in using the maximum-minimum method andomittingxthe filter and am lier in using the binaural method.

4. In combination, a compressional wave pickup system including aplurality o f spaced pick-up units and a telephone means associatedtherewith, means for adjusting said system to bring the energy atthetelephone means into substantially the same phase and create therebyan observable intensity maximum and means for filtering out the lowerwave frequencies from the received energy whereby the maximumobservation may be sharpened.

5. A method of increasing the accuracy of determining the direction of asource of mixed sound waves which consists in receiving the waves at aplurality of points spaced from one another, translating the waves soreceived into corresponding electrical impulses of the same frequencyand character, conducting said translated waves to a common point,variably retarding the progress of the waves until said waves arebrought in the same observable phase, ltering. the waves brought to thecommon point to pass only the higher frequencies picked up from thesource whereby the accuracy of determination of the phase coincidencemay be more accurately observed.

6. A method of increasing the accuracy of determining the direction of'a source of mixed sound Waves 4which' consists first in receiving thesound waves at a plurality of points spaced apart one. from the other,transmitting the energy so received to a common point, variablyretarding the time of transmission of the energy to the comto saidcommon point mon point untilall of the energies have approximately thesame observable time phase, ltering the energy after retardation toeliminate the lower frequencies from the source that is being observedand further adjusting the retarding of the 5 impulses to make a moreaccurate observation of the direction of the source.

7. A method of increasing the accuracy `of determining the direction `ofa source of mixed sound waves which consists in receiving sound at 10 aplurality of points spaced apart one fromv .the other, transmitting theenergy picked up at all of said points to a common center, variablyretarding energy so picked up until a maximum intcnsity of energyisl/observed, filtering out the l5 lower sound frequencies of the sourcelistened to after the energy has been retarded and varying theretardation until a sharper maximum is obtained.

8. A method of increasing the accuracy of de- 20 termining the directionof a source of mixed sound waves which consists rst in receiving thesound waves at a plurality of points spaced apart one from the other,transmitting the energy so received to a common point, variablyretarding l 20 the time of transmission of the energy to the commonpoint until all of the energies have approximately the same observabletime phase, ltering the energy after retardation to eliminate the lowerfrequencies from the source that is being ob- 0 served and furtheradjusting the retarding of the impulses to make a. more accurateobservation of the direction of the source, the filter being adapted tolter out frequencies below a value not sub- Vand further adjusting thestantially less than 800 cycles arriving from the source of sound;

9. A method of increasing the accuracy of determining the direction of asource of mixed sound waves which consists in receiving the sound at aplurality of points spaced one from the other,-

conducting the energy received at the spaced points to a common center,variably retardlng the time of such. conduction until the energiesproduce at the central point an observable maximum, filtering out thelower sound frequencies of the source received and adjusting theretardation for a sharper maximum, then listening at the central pointby the binaural method to determine whether a true maximum has beenobtained.

10. A method of increasing the accuracy of determining the direction ofa source of mixed sound waves which consists rst in receiving the soundwaves at a plurality of points spaced apart one from the other,transmittingthe energy sc received to a common point, variably retardlngthe time of transmission of the energy to the common point until all ofthe energies have approximately the same observable time phase, lteringthe energy after retardation to eliminate the lower frequencies from thesource that is being observed retarding of the impulses to make a moreaccurate observation of the direction of the source, the lter lteringout all frequencies below 1500 cycles whereby the frequencies o f thesound source above this value are observed.

WILLY KUNZE.

